Field of the Invention
This invention relates generally to high frequency amplification devices and more particularly to such a device where amplification results from interaction of electron beams with RF fields in wave propagation transmission lines.
Interaction types of devices for amplification of RF signals at microwave frequencies are well known. The traveling wave tube constitutes one such device wherein a longitudinal electron beam interacts continuously with the RF fields of a wave traveling along a slow wave propagating structure such as a helix. Additionally, means are provided to couple an external RF signal to and from the slow wave structure. The velocity of the electron beam, moreover, is adjusted to be approximately the same as the phase velocity of the wave propagating on the helix. When an RF wave is launched on the helix, the longitudinal component of the field interacts with the electrons traveling along in approximate synchronism with it. Some electrons will be accelerated while others will be decelerated, resulting in a progressive rearrangement in phase of the electrons with respect to the wave. The electron beam is thus modulated and induces RF fields on the helix. This process of mutual interaction continues along the length of the helix with the net result being that direct current energy is given up by the electrons to the traveling wave as radio frequency energy and the RF signal is thus amplified.
One example of a traveling wave tube is shown and described in U.S. Pat. No. 3.760,219, issued to Charles M. DeSantis, et al., one of the present inventors on Sept. 18, 1973. This patent discloses, among other things, a traveling wave tube having a control grid for producing klystron type of bunching of the electron stream. Another known type of microwave amplification device, which employs transverse field interaction for its operation, comprises a multibeam klystron which has been disclosed and described, for example, in a U.S. Army Ecom technical report entitled, "High Power Traveling Wave Multiple Beam Klystron", Ecom-0007F Technical Reoort, October, 1967, D.A. 28-043AMC-00007(e). There, two and three waveguide multiple beam klystron structures are shown and described that produce megawatts of power over a wide frequency band and at substantially lower beam voltages relative to single beam conventional klystrons. The multiple beam klystron utilizes a multiplicity of separate distinct electron beams that are arranged to transversely interact with RF fields in at least two more waveguides that are periodically loaded with capacitive gaps consisting of both buncher and catcher type gaps. The buncher gaps are driven by transverse RF waves traveling in one waveguide where the wave in turn modulates each of the beams. The beams then travel across the catcher gaps in the other waveguide where an amplified RF wave is induced therein and which is conveyed to an output circuit.
In the related application referenced above, a transverse field interaction multibeam amplifier device is disclosed comprised of a structure having a plurality of discrete cathode elements cylindrically located in succession along a central axis of RF propagation and wherein a respective number of annular collectors are located outwardly from the cathodes within a cylindrical housing structure. Intermediate the cathode and collector elements are two additional cylinders, one having a relatively smaller diameter than the other, but the smaller diameter cylinder including respective number of annular grids, while the larger cylinder comprises a structure having a corrugated or undulating slow wave wall surface structure and a respective number of apertures in the form of annular slots formed therein. The cathodes emit radial beams of electrons which pass through and are bunched by the adjoining grids and then accelerated by the slots to the collectors while interacting with and being modulated by an input beam propagating along the central axis of the cylindrical structure between a first pair of walls, for example, including the grids and cathodes and inducing an output beam in a second pair of walls, for example, including the grids and the cylinder including slow wave wall surface structure.
It is an object of the present invention, therefore, to provide an improvement in apparatus for amplifying electromagnetic waves.
It is a further object of the invention to provide an improvement in devices for amplifying microwave signals.
It is another object of the invention to provide improvement in microwave amplification devices which operate on the principle of field interaction between an electron beam and an RF signal propagating along a transmission line.
It is yet another object of the invention to provide improvement in field interaction amplification devices which are adapted to provide broadband operation.